The Acquisition

This is a pretty basic blog of the resto of this little N26. I acquired this as a non runner but smostlyy complete. It lacked a speedo but someone had started to sort it so it turned over and the frame had been painted. I hadn't really meant to buy this bike and probably shouldnt have but it seemed fairly straightforward to get this one back on the road. Here's some general shots of the bike.

 

Preliminary assessment showed;

1. No spark it will need new points and the magneto testing.

2. fuel tap is blocked... it will need a carb and tank clean

3. Both tyres badly worn so new tyres and tubes needed.

4. Wheel bearings front and rear are very rough, brakes are poor

5. Chain and sprockets are very badly worn

6. Horn/dip control broken

The mudguards will need repainting.

Most if these jobs are described in other of my blogs but this bike threw a few curve balls. It's been through a lot and many of the parts I found weren't contemporary with the original bike.

Front wheel

Front wheel is straightforward to remove (see S23 blog).. the hubs are dismantled by removing the brake plate nut. Apply the brake lever to prevent plate rotation.

The brake plate then lifts out with the shoes on the rear

These hubs use the horse-shoe spring

Which clips beneath the shoes at its apex.

There was plenty of shoe thickness, but sadly corrosion had attacked the shoes which were now brittle. I relined them using NOS linings and rivets. 

I did also check the bearings and the wheel did feel a little rough as it spins so I will deal with these later.

Rear Wheel

Removing rear wheel is more complex.. you need to remove the drive chain by splitting it at the removeable link.

The rear mudguard and rack have several stays all bolting to the rear arm. I may need to remove these so I have photographed them for the record.

There is also a mudguard fixing to the frame at the front. I decided to remove the mudguard as well as the wheel eventually as its pretty rusty and needs attention.

Essentially, loosen the rear wheel spindle nuts on the right and tap the spindle thrugh- this releases the chain tensioners both sides and the spacer on the right.. keep them on the axle to prevent loss. The wheel will then come off and the rest of the mudguard fixings can be removed as well.

As before loosen the hub nut by applying the brake lever.

Here you can see the terrible state of the sprocket teeth.

The brake plate then lifts away as in the front wheel carrying the shoes with it. Note lever spring position.

...and the arrangement of the shoe springs. There are 2 coil springs i the rear hub.. note that the spring hooks are arranged one-up, one-down. This "feels" right but I dont know if it is.

There are also retainers fitted in the hub which locate over the centre of the shoes- presumably to prevent them flexing. They seem a sensible addition but Ive not seen such a thing before. However, the main effect they have is to make it harder to remove the shoes as the usual bend together approach cant be used and its necessary to remove at least one spring hook to release the tension.

Turning to the hub itself, this is a half-width hub and of a type Ive not found before. This is an early hub (Type 1) that would not have been fitted originally to a bike of this year. It must have been swapped out by a PO. The hub has a prominent circlip which the manual recommend removing before working on the hub oer bearings. I cant see why as it appears totally functionless. A forum member advises me that its a saftey feature to prevent spoke ends dropping into the brake if a spoke should break. That is possibly true but spoke breakage is a rare event and this seems an elaborate means to prevent it... especially as the rear drive sprocket on this wheel- which can certainly be expected to wear in the life of the bike, is non-removeable and welded in place! Why would a designer worry about rare spoke effects and ignore a very real need for effective maintenance.

I did actually remove the bearings from the hub before the circlip.. its not necessary to do this as the circlip seems to have no effect and you can tackle circlip and bearings in any order you prefer. However  I'll present the circlip stuff here whilst I'm addressing it... The circlip just lifts out at the join and is released from the retaining lugs as its compressed towards the hub centre

Removing the circlip exposes the spoke heads and the sprocket weld lugs.

Obviously it's not a simple job to change the sprocket. I was forced to get a second hand hub from tjis type of wheel which had a good sprocket. I used a local wheel builder to swap hubs using the original rim and spokes.... I liked the brass nipples on these. This worked really well... I replaced 2 broken spokes at the same time.  It did mean that I needed to address the bearings in the new hub so I swapped these out (see wheels sipplemental).

Bearings

Front wheel bearings.

This bike uses cone and cup bearings- highly primitive. Hold one and unscrew the other. The manual seems to have this confused but I found you need to hold the left side (sprocket side) and unscrew the right.

This unscrews the central spacer tube so that the two cones are detached from one another. Check that the right hand side is free to move in and out and then tap the left (sprocket-side) bearing out using a flat ended drift. alth

This will bring out the spindle cup, caged bearing and oil seal which remain attached together..

Reverse the drift to tap out the right hand side spindle cone- its only really held by the oil seal so it doesn't take much.

 you can then tap out the bearing which will bring the oil seal with it. In my case, these didn't look pretty. The bearings are 1/4" imperial bearings and there are 10 to a cage, whilst the oil seal is a 18x30.2x5 size. Both of these are very hard to find from suppliers other than the NSU specialists and consequently both are very expensive. Im trying a W125068025R23 which is an imperial size close fit   11/16x1/.25x1/4"... Ill let you know if it works! The bearings do not need the cage which is only there to make assembly easier, so if I can't find a cheaper source, I'll assemble using loose bearings... bit of a faff but as there may be room for an extra ball it could even help load bearing. In fact I found its. Simple process to press the balls out of the cage and press new balls in. It needs only firm finger pressure.

The left hand cone can be further dismantled to remove the spacer tube by holding the flat faced section in a vice and using grips to rotate the spacer tube. The bearing cage and oil seal with then pull off.

I cleaned up all parts of the bearing.. some obvious pitting to the cones and some of the bearings were badly corroded, I will change these.

I did buy new cones and spindles eventually as refitting these even after polishing didn't really help.

Fuel Tap

This bike came with a fuel tap in fragments. NSU replacements are expensive so I sought a suitable substitute. The thread is an M12 1.0 pitch. I'll need to clean those on the tank but I did find an alternative tap which even has an internal settlement chamber. This is intended for the Hercules Mk2 ultra K50 but it fits well and I'll let you know how it turns out in use. This has worked well so far.

Wiring Loom

The wiring loom in this bike had been cut and luckily I have a replacement. The recommended method is to tie a line to the existing wires and use this to pull the new loom through. I found that this was impossible owing to an obstruction inside the rear arm. It was relatively easy to poke both the clutch cable and the loom down through the opening in the frame near the handlebars although it did take a little fiddling around the air filter before I could get both the wire for the magneto and clutch cable out of opposite sides of the frame using the cut-out above the motor for this purpose. It was however impossible to feed the rear light wire through the rear lh fork as there was an obstruction that meant the sleeving over this wire could not pass through. In the end I was forced to remove the sleeving and pass a single wire through the fork to supply the rear light. I did end up removing the motor but in fact this didnt help at all as those parts of the frame that you need to access are sealed.

Clutch and loom exiting the frame into the cut-out above the motor. The grey rear light wire still has to be fed along the rear fork

Clutch cable exiting to cut-out towards the left side of the motor.

Gear change twistgrip.

The twistgrip suffered from the usual problem of missing detent ball so it was loathe to locate in each gear position. I removed the cable enf

and then removed the twistgrip from the bars and took a number of photographs to show how the armature and decompression lever are fitted. The two sections can then be separated.

Note the grub screw over the detent spring 

...and the decompression lever removed.

Decompression lever fittings

I removed the grub screw and the  detent spring was still present although the ball was missing.

Grub screw and spring removed.

I have tried to machine a new ridge to retain a larger ball several times before and it always fails. Accordingly to replace the detent I simply drilled through to M5 and tapped the hole to M6. I could then fit an M6 ball detent pin and adjust the position for satisfactory operation once the control is reassembled. This sorted the issue and I was very pleased with the result. The twistgrip however also suffers from the usual wear to the "wing tabs" on the clutch lever. These shoukd interdigutare between the lugs on the twistgrip to act as a second lock (in addition to the detent) and hold the bike in gear. These wings nearly awats wear and when this happens the bike can jump out or into gear if the twistgrip isn't held in position. This means I really need a new clutch lever as I've found repairing this to be impossible. Maybe a skilled TIG welder could build up the ally here? I've ordered a new lever.